Chrome-free etch solutions for chemically resistant polymer materials

ABSTRACT

Chemically resistant polymers are etched using a chrome-free etch solution which is aqueous and alkaline. The chrome-free etch aqueous alkaline solution is environmentally friendly and can be used in the preparation of chemically resistant polymers for electroless metal plating including the plating of through-hole walls in the manufacture of printed circuit boards.

FIELD OF THE INVENTION

The present invention is directed to chrome-free etch solutions andmethods for etching chemically resistant polymer materials. Morespecifically, the present invention is directed to chrome-free etchsolutions and methods for etching chemically resistant polymermaterials, wherein the chrome-free etch solutions are aqueous alkalinesolutions and are environmentally friendly and the chemically resistantpolymer materials include acrylonitrile butadiene styrene, acrylonitrilebutadiene styrene-polycarbonate or combinations thereof.

BACKGROUND OF THE INVENTION

Prior to electroless metallization a substrate surface containingorganic polymers is typically etched with an etch solution to achievegood adhesion between the substrate surface and electroless platedmetals. Chemically resistant polymers such as, for example,acrylonitrile butadiene styrene and acrylonitrile butadienestyrene-polycarbonate are highly desirable for articles and productswhich are electroless metal plated; however, such polymers are resistantto many chemicals used in etch solutions. Although they are “attacked”by concentrated sulfuric acid and nitric acid, acrylonitrile butadienestyrene and acrylonitrile butadiene styrene-polycarbonate tend to beresistant to aqueous acids, alkalis, concentrated hydrochloric andphosphoric acids and alcohols. Acrylonitrile butadiene styrene andacrylonitrile butadiene styrene-polycarbonate have been successfullyetched with etching solutions of hexavalent chromium or Cr(VI). However,such etching solutions are toxic and environmentally unfriendly. Etchsolutions of Cr(VI) present undue hazards to workers in the plating artsas well as the environment. Although great efforts have been made overthe years by many chemical suppliers and the plating industry to replacecurrently used toxic etching solutions, no satisfactory commercialproduct which is free of Cr(VI) is currently available on the market.

Cr(VI) containing compounds are suspected of being cancer-causing.Accordingly, dealing with these compounds is subject to strictenvironmental regulations. For example, in the European Union theregulation Registration, Evaluation, Authorization and Restriction ofChemicals, known as REACh, has banned numerous chemicals. In the face ofthe potential dangers caused by Cr(VI) releasing compounds, aprohibition of the industrial use of Cr(VI) containing compounds cannotbe excluded. In addition, Cr(VI) containing etches often includeconcentrated sulfuric acid and must be used very carefully. The acid ishighly corrosive and disposal is expensive.

Concentrated sulfuric acid without Cr(VI) has also been used as anetchant such as in a solution conventionally known as “Piranha”solution. This solution is a 3:1 mixture of concentrated sulfuric acidwith hydrogen peroxide. This is an extremely exothermic mixture andbecomes hot when the hydrogen peroxide is added to the sulfuric acid. Ingeneral, working with sulfuric acid is hazardous. Sulfuric acid fumesare toxic and have target organ effects on skin, respiratory,reproductive systems and fetal tissue.

Over the years a variety of chemical species have been suggested in theindustry for use as chrome-free oxidizing agents in wet etchingprocesses to modify organic polymer surfaces. Such oxidants includeMn(VII), Mn(VI), Mn(IV), Ce(IV), persulfate, organic solvents such asdioxane, metal halogenides and nitrates of Fe, Cu, Ti, Zn, and Mg.Oxidizing agents are consumed either by the etching process or due tothe instability of the oxidants. Therefore, frequent replenishing or are-generation method is needed. Re-generation methods are especiallypreferred for industrial settings. Mn(VII) is one of the most commonlyused oxidizing agents. In solution it is typically in the form of ionicspecies MnO₄ ⁻. Electrochemical regeneration of Mn(VII) in alkalinesolutions has been used in different industries, such as in themanufacture of circuit boards. In acidic media re-generation of Mn(VII)appears more difficult than in an alkaline medium.

However, either in an acidic or alkaline medium, Mn(VII) is unstable andtends to reduce to its lower oxidation states, especially to Mn(IV),consequently forming a large quantity of the insoluble MnO₂ and causingquality issues on the treated polymer surfaces. Frequent removal of MnO₂precipitation from the permanganate etching solution is thereforerequired in the industrial scale operation. Therefore, such etchsolutions are inadequate to meet the demands of the metal platingindustry for polymer preparation for electroless metallization,including electroless metallization of chemically resistant polymers,such as acrylonitrile butadiene styrene and acrylonitrile butadienestyrene-polycarbonate.

Accordingly, there is still a need for a method of etching chemicallyresistant polymer materials such as acrylonitrile butadiene styrene andacrylonitrile butadiene styrene polycarbonate which is efficient,provides good surface roughening in preparation for electrolessmetallization, and is both worker and environmentally friendly.

SUMMARY OF THE INVENTION

The present invention is directed to a method including: providing asubstrate including one or more organic polymers chosen fromacrylonitrile butadiene styrene and acrylonitrile butadienestyrene-polycarbonate; providing an aqueous alkaline etch solutioncomposed of hydrogen peroxide and one or more sources of hydroxide ions;and applying the aqueous alkaline etch solution to the substrate to etchat least the one or more organic polymers chosen from acrylonitrilebutadiene styrene and acrylonitrile butadiene styrene-polycarbonate.

The methods of the present invention enable efficient etching ofchemically resistant polymer materials such as acrylonitrile butadienestyrene and acrylonitrile butadiene styrene-polycarbonate to provide arough surface for the chemically resistant polymer materials inpreparation for electroless metallization. The surface of the chemicallyresistant polymer materials as etched by the methods of the presentinvention enables good metal adhesion to the chemically resistantpolymer material. Accordingly, metals electrolessly plated on the etchedchemically resistant polymer materials have good peel strength. Theprobability of adhesion failure and blistering between the surface ofthe etched polymer material and the electrolessly plated metal layers issubstantially reduced. Since blistering can propagate even duringelectrolytic metal plating stages subsequent to electroelss metalplating, the methods of the present invention also improve adhesion ofelectrolytic deposits. Further, the aqueous alkaline etch solution ofthe present invention is a chrome-free etch solution, free of hazardousacids, such as sulfuric acid and nitric acid, and is also apermanganate-free etch. The aqueous alkaline etch solution of thepresent invention is both worker and environmentally friendly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a metallized ABS-PC coupon that has beenpre-treated only with an aqueous alkaline composition of the presentinvention and not treated with a solvent swell.

FIG. 2 is a photograph of a metalized ABS-PC coupon that has not beenpre-treated with an aqueous alkaline composition of the presentinvention and also has not been treated with a solvent swell.

FIG. 3 is a SEM at 25,000 X of a cleaned and solvent swelledacrylonitirile butadiene styrene polymer surface.

FIG. 4 is a SEM at 23,800 X of an acrylonitrile butadiene styrenepolymer surface cleaned, treated with a solvent swell and an aqueousalkaline etch solution of the present invention.

FIG. 5 is a SEM at 12,300 X of an acrylonitrile butadiene styrenepolymer surface cleaned, treated with a solvent swell and a chrome (VI)acid etch.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification, the abbreviations given belowhave the following meanings, unless the context clearly indicatesotherwise: ° C.=degrees Centigrade; g=gram; L=liter; M=molar ormoles/liter; mL=milliliters; g/L=grams per liter; m=meters;cm=centimeter; mm=millimeters; μm=microns; N/cm=Newtons per centimeter;Newtons=1 kilogram meter per second squared; kN=kilo-Newton; wt%=percent by weight; DI=deionized water; ABS=acrylonitrile butadienestyrene; ABS-PC=acrylonitrile butadiene styrene polycarbonate;Cr(VI)=chromium six oxidation state; sulfuric acid=H₂SO₄; hydrogenperoxide=H₂O₂; EO/PO=ethylene oxide/propylene oxide; potassiumdichromate=K₂Cr₂O₇; EDTA=ethylenediaminetetraacetic acid; ammoniumhydroxide=NH₄OH; and SEM=scanning electron microscope.

All amounts are percent by weight and all ratios are by weight, unlessotherwise noted. The terms “a” and “an” are understood to include boththe singular and the plural. The term “solvent swell” or “solventswelling” means contacting an organic polymer with a solvent such thatthe polymer does not completely dissolve in the solvent but ratherabsorbs a portion of the solvent such that it subsequently swells orincreases in volume. The term “chemically resistant polymer” means anorganic polymer or organic copolymer where surface morphology is notreadily modified, such as roughened or textured, upon exposure tochemicals such as aqueous acids, alkalis, concentrated hydrochloricacid, phosphoric acid and alcohols. The term “modified” means alteringthe physical, chemical or both physical and chemical characteristics ofthe surface from its initial physical or chemical or both physical andchemical characteristics. The term “surface morphology” means shape,texture and distribution of materials at the surface. The term “matte”means dull or lack of luster. The term “polymer” as used in the presentapplication includes copolymer. The terms “roughen” and “texturize” areused interchangeably throughout the present specification. The term“gemini surfactants (dimeric surfactants)” means surfactants which havetwo hydrophilic head groups and two hydrophobic groups in the molecule.The term “aqueous based” or “aqueous” means that the composition'ssolvent is water. The term “miscible” means capable of being mixed toprovide a substantially stable composition such that the mixedcomponents do not readily separate into their original components withina desired time period for their desired function. Acrylonitrilebutadiene styrene and acrylonitrile butadiene styrene polycarbonate arethermoplastic polymers. All numerical ranges are inclusive andcombinable in any order, except where it is logical that such numericalranges are constrained to add up to 100%.

Substrates of the present invention include one or more chemicallyresistant polymers. Preferably, such chemically resistant polymers arechosen from one or more of ABS and ABS-PC. More preferably, thesubstrates of the present invention include ABS, even more preferably,the substrates of the present invention are composed of one or more ofABS and ABS-PC, still more preferably the substrates of the presentinvention are composed of ABS. The substrates of the present inventioncan be incorporated in various types of articles where electroless metalplated substrates which include one or more of electroless metal platedABS and ABS-PC are desired.

Prior to metallization, at least one of ABS and ABS-PC are treated withan aqueous alkaline etch composition composed of hydrogen peroxide, oneor more sources of hydroxide ions and water to roughen or texturizesurfaces of the ABS and ABS-PC of the substrate.

Prior to electroless metallization and etching of the substrates of thepresent invention, optionally, but preferably, the substrates can becleaned using conventional cleaning compositions known in the art andliterature to clean polymer materials prior to metallization.Preferably, such cleaning compositions are alkaline. More preferablysuch cleaning compositions have a pH equal to or greater than 9, evenmore preferably, such cleaning compositions have a pH of 9-12.Preferably, such alkaline compositions are aqueous based, or they aremixtures of water and one or more aqueous soluble or aqueous miscibleorganic solvents. Such alkaline cleaning compositions can include one ormore amines, one or more surfactants and one or more of aqueous ororganic solvents.

Amines include, but are not limited to, alkanolamines which include, butare not limited to, monoethanolamine, diethanolamine andtriethanolamine; hydroxylamines; tertiary amines such as, but notlimited to, trimethylamine and EDTA. Such amines can be included in thecleaning compositions in conventional amounts as are well known to thoseof skill in the art. Many of the amines are commercially available andcan be obtained commercially from Sigma Aldrich-Aldrich Fine Chemicals(Milwaukee, Wis.) or they can be prepared from processes known in theart or in the chemical literature. Preferably, such amines are includedin amounts of at least 0.1 g/L and greater, more preferably, from 0.5g/L to 10 g/L.

Various conventional surfactants well known in the art can be includedin the cleaning compositions, such as anionic, cationic, amphoteric,nonionic, gemini surfactants, or combinations thereof. Many of theconventional surfactants are commercially available from Sigma Aldrichor can be prepared from processes known in the art or in the chemicalliterature. There is no preferred surfactant or combination ofsurfactants. An example of typical nonionic surfactants include, but arenot limited to, alkoxy polyoxyethylene ethanol surfactants wherein thealkoxy is preferably of 10-20 carbon atoms and the ethylene oxidecontent is preferably 6-20 moles per mole of surfactant molecule. Suchnonionic surfactants are commercially available under the TradenameSURFONIC® J-40 surfactant formulation (available from Alchem ChemicalCompany). Examples of other nonionic surfactants are the polyoxyethylenearyl ethers. An example of a commercially available surfactantformulation which includes polyoxyethylene aryl ethers is SURFONYL™ 104Egemini surfactant formulation (available from Air Products). EO/POnonionic surfactants can also be included. Such EO/PO nonionicsurfactants are described in more detail below. The various surfactantscan be included in conventional amounts used to clean polymer materialsprior to electroless metallization. Preferably, surfactants can beincluded in amounts of 0.5 g/L or greater, more preferably, in amountsof 1 g/l to 15 g/L.

Cleaning is done, for example, by spraying or immersing the substrate inthe cleaning composition for a sufficient amount of time to adequatelyclean the polymer material. Preferably, the substrate is cleaned for2-10 minutes at temperatures from 30-70° C. After cleaning, thesubstrate is optionally rinsed with DI water.

Prior to metallization and etching, and after cleaning the substrates,optionally, but preferably, the substrates are then swelled with asolvent swell to increase the volume of the polymer material in furtherpreparation for etching with an aqueous alkaline etch composition of thepresent invention. Solvent swells used to treat the chemically resistantpolymers of the present invention include one or more organic solvents,optionally water, and one or more surfactants and, optionally, one ormore additives to assist in swelling the chemically resistant polymers.

Organic solvents include, but are not limited to, glycols, glycolethers, glycol ether acetates, alkylene carbonates and ketones. Examplesof glycols which can be used to swell the chemically resistant polymersof the present invention are ethylene glycol, diethylene glycol,triethylene glycol, polyethylene glycol, propylene glycol, dipropyleneglycol, tripropylene glycol and polyprolylene glycol. Examples of glycolethers which can be used to swell the chemically resistant polymers ofthe present invention are diethylene glycol monomethyl ether, diethyleneglycol monopropyl ether, diethylene glycol monobutyl ether, ethyleneglycol monomethyl ether, ethylene glycol phenyl ether, dipropyleneglycol monomethyl ether, dipropylene glycol monopropyl ether anddipropylene glycol monobutyl ether. Examples of glycol ether acetatesare dipropylene glycol monomethyl ether acetate, propylene glycolmonomethyl ether acetate and propylene glycol phenyl ether acetate.Examples of alkylene carbonates are ethylene carbonate and propylenecarbonate. Examples of ketones are acetone, hexanone and pentanone.Preferably, the solvent is chosen from glycols ethers, alkylenecarbonates and ketones. More preferably, the solvent is chosen fromalkylene carbonates and ketones. Even more preferably, the solvent ischosen from alkylene carbonates and acetone. Most preferably, thesolvent is chosen from alkylene carbonates of which the preferredalkylene carbonate is propylene carbonate. Such solvents are included inthe solvent swell in amounts of at least 50 g/L, preferably, from 50 g/Lto 150 g/L.

Surfactants included in the solvent swell can be one or more of anionic,cationic, amphoteric, nonionic and gemini surfactants. Surfactants canbe included in conventional amounts. Preferably, surfactants can beincluded in the solvent swells in amounts of at least 0.1 g/L, morepreferably, from 0.5 g/L to 10 g/L. Even more preferably, the solventswell includes one or more EO/PO nonionic polymer surfactants. The EO/POpolymers can be block or random. Examples of commercially availableEO/PO polymer surfactants are the PLURONIC™ polymers available fromBASF. The PLURONIC™ polymer tradename refers to poloxamers which arenonionic tailback copolymers composed of a central hydrophobic chain ofpolyoxypropylene flanked by two hydrophilic chains of polyoxyethylene. Ageneral chemical name for such copolymers is α-hydroxy-ω-hydroxypoly(oxyethylene)_(x)poly(oxypropylene)_(y)poly(oxyethylene)_(z), wherein xis from 5-200, y is from 5-100 and z is from 5-200. Poloxamers can havemolecular weights from about 2000 to about 20000 daltons. Examples ofcommercially available poloxamers are PLURONIC™ L-10, L-84, L-101,L-121, L-31, L-35, L-43, L-44 and L-64 surfactants. Additional additiveswhich optionally can be included in the solvent swells include, but arenot limited to, lactones. Lactones include, but are not limited to,γ-butyrolactone, ϵ-caprolactone, γ-caprolactone and γ-valerolactone.Such lactones can be included in the solvent swells in amounts ofpreferably from 0.5 g/L to 10 g/L, more preferably, from 1 g/L to 5 g/L.

The solvent swell is applied to the substrate, for example, by sprayingor immersing the substrate in the solvent swell for a sufficient time toswell or increase the volume of the polymer material to be etched.Preferably, the substrate is treated with the solvent swell for 1-5minutes at temperatures from 30-70° C. The solvent swell treatedsubstrate is then optionally rinsed with DI water and then etched withthe aqueous based alkaline etch composition of the present invention.

The aqueous alkaline etch composition of the present invention iscomposed of sufficient amounts of hydrogen peroxide, one or more sourcesof hydroxide ions and water to etch at least one of ABS and ABS-PC.Preferably, the aqueous alkaline etch composition includes 5 g/L to 20g/L hydrogen peroxide. More preferably, hydrogen peroxide is included inthe etch composition in amounts of 10 g/L to 15 g/L, even morepreferably, from 12 g/L to 15 g/L. One or more sources of hydroxide ionsinclude, but are not limited to, alkali metal hydroxides, alkaline earthmetal hydroxides, ammonium hydroxide and quaternary ammonium hydroxides.One or more sources of hydroxide ions are preferably included in theaqueous alkaline composition of the present invention in amounts of 5g/L to 30 g/L, more preferably, from 10 g/L to 20 g/L, even morepreferably, from 15 g/L to 20 g/L. A pH of the aqueous alkalinecomposition of the present invention ranges from 10 or greater,preferably from 11 to 14, more preferably, from 12 to 14, still morepreferably, from 12.5 to 14, most preferably, from 12.5 to 13.5.

Alkali metal hydroxides include sodium hydroxide, potassium hydroxide,lithium hydroxide and cesium hydroxide. Preferably, the alkali metalhydroxide is sodium or potassium hydroxide. More preferably, the alkalimetal hydroxide is sodium hydroxide. Preferably, the alkaline earthmetal hydroxide is calcium hydroxide. Preferably, quaternary ammoniumhydroxides are chosen from (C₁-C₈)alkyl quaternary ammonium hydroxide,more preferably, the quaternary ammonium hydroxides are chosen from(C₁-C₄)alky quaternary ammonium hydroxides, even more preferably, thequaternary ammonium hydroxides are chosen from (C₁-C₂)alky quaternaryammonium hydroxides. Most preferably, the quaternary ammonium hydroxideis tetramethylammonium hydroxide (TMAH or TMAOH). The preferred sourceof hydroxide ions of the present invention is chosen from sodiumhydroxide, potassium hydroxide, calcium hydroxide and TMAH. Morepreferably, the source of hydroxide ions of the present invention ischosen from sodium hydroxide and TMAH. The most preferred source ofhydroxide ions is sodium hydroxide.

Preferably, the aqueous alkaline etch composition is composed ofhydrogen peroxide, one or more sources of hydroxide ions chosen fromalkali metal hydroxides, alkaline earth metal hydroxides, ammoniumhydroxide and quaternary ammonium compounds, counter cations of the oneor more sources of hydroxide ions and water. More preferably, theaqueous alkaline etch composition is composed of hydrogen peroxide, oneor more sources of hydroxide ions chosen from sodium hydroxide,potassium hydroxide, calcium hydroxide, ammonium hydroxide and(C₁-C₈)alkyl quaternary ammonium hydroxide, counter cations of the oneor more sources of hydroxide ions and water. Even more preferably, theaqueous alkaline compositions are composed of hydrogen peroxide, one ormore sources of hydroxide ions chosen from sodium hydroxide, ammoniumhydroxide and (C₁-C₄)alkyl quaternary ammonium hydroxide, countercations of the one or more sources of hydroxide ions and water. Stillmore preferably, the aqueous alkaline etch composition is composed ofhydrogen peroxide, one or more sources chosen from sodium hydroxide,ammonium hydroxide and TMAH, counter cations of the one or more sourcesof hydroxide ions and water. Most preferably, the aqueous alkaline etchcomposition is composed of hydrogen peroxide, sodium hydroxide as asource of hydroxide ions, sodium counter cations and water, wherein a pHis 12.5-13.5.

The substrates are etched with the aqueous alkaline etch composition ofthe present invention, for example, by spraying or immersing thesubstrate in the aqueous alkaline etch composition for 2 minutes to 15minutes, preferably, from 5 minutes to 10 minutes. The temperature ofthe aqueous alkaline etch composition during etching is from 30-90° C.,preferably, from 40-80° C., more preferably, from 50-80° C. The etchingmethod of the present invention alters the surface morphology of polymermaterials such as ABS and ABS-PC to roughen or texturize at least theABS, ABS-PC or combinations thereof of the surface to provide crevicesor pores in at least the ABS, ABS-PC or combinations thereof.

Although the substrates of the present invention include ABS, ABS-PC orcombinations thereof, the substrates of the present invention caninclude one or more additional polymer materials which the aqueousalkaline etch solution can etch. Such additional polymer materialsinclude, but are not limited to, thermoplastic resins such as acetalresins, acrylics, such as methyl acrylate, cellulosic resins, such ascellulose acetate, cellulose propionate, cellulose acetate butyrate andcellulose nitrate, polyethers, nylon, polyethylene, polystyrene, styreneblends, polychlorotrifluoroethylene, and vinylpolymers and copolymers,such as vinyl acetate, vinyl alcohol, vinyl butyral, vinyl chloride,vinyl chloride-acetate copolymer, vinylidene chloride and vinyl formal;thermosetting resins such as allyl phthalate, furane,melamine-formaldehyde, phenol-formaldehyde and phenol-furfuralcopolymers, alone or compounded with butadiene acrylonitrile copolymersor acrylonitrile-butadiene-styrene copolymers, polyacrylic esters,silicones, urea formaldehydes, epoxy resins, allyl resins, glycerylphthalates and polyesters. It is preferred that the organic polymercomponents of the substrates of the present invention are composed ofABS, ABS-PC or combinations thereof. More preferably, the organicpolymer components of the substrates of the present invention arecomposed of ABS or ABS-PC, most preferably, the organic polymercomponents of the substrates of the present invention are composed ofABS.

After at least the ABS, ABS-PC or combinations thereof are etched, thesubstrate is optionally rinsed with water. The substrate is then,optionally, further treated for reception of a catalyst for catalyzingelectroless metal plating using conventional processes known in the artfor electroless metallization. Conventional catalysts can be used tocatalyze the electroless metal plating. Such catalysts include, but arenot limited to, colloidal and ionic catalysts. Such catalysts include,but are not limited to, one or more noble metals such as gold, silver,platinum and palladium. Preferably, the one or more noble metals arechosen from silver and palladium. More preferably, the catalyst metal ispalladium. The metals of the catalysts can be applied in their reducedmetal state or, in the case of ionic catalysts, they are applied intheir ionic state, such as palladium (II) and silver (I). Preferably,the catalyst metal ions are palladium (II) ions.

When the catalyst is a colloidal catalyst, preferably, a tin-palladiumcatalyst is used. Such tin-palladium catalysts are well known in the artand disclosed in the electroless metal plating literature. Acommercially available tin-palladium catalyst is CIRCUPOSIT™ 3344tin-palladium catalyst (available from Dow Electronic Materials,Marlborough, Mass.).

When the catalyst is an ionic catalyst, preferably, an aqueous alkalinepalladium (II) catalyst is used. Such aqueous alkaline palladium (II)catalyst include one or more complexing agents which stabilize thecatalyst prior to application to the substrate. Such complexing agentsinclude, but are not limited to, pyrazine derivatives, such as,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2,5-dimethylpyrazine,2,3,5-trimethylpyraizine, 2-acetylpyrazine, aminopyrazine,ethylpyrazine, methoxypyrazine, and 2-(2′-hydroxyethyl)pyrazine. Molarratios of complexing compounds to metal ions can range from 1:1 to 4:1.Such ionic catalysts are known in the art or can be obtained from theelectroless metal plating literature.

In preparation for reception of the colloidal or ionic catalyst, thesubstrate with the etched organic polymer material is conditioned. Theetched organic polymer material which includes at least ABS, ABS-PC orcombinations thereof can be conditioned with one or more conventionalconditioners known in the art. The substrate containing the etchedpolymers is, for example, sprayed or immersed in the conditioner attemperatures of 30-90° C., preferably, from 40-80° C. The substrate iscontacted with the conditioner for 2-10 minutes. Examples ofcommercially available acid conditioners are CIRCUPOSIT™ Conditioners3320 and 3327 solutions (available from Dow Electronic Materials).Examples of commercially available alkaline conditioners are CIRCUPOSIT™Conditioner 231, 3325, 813 and 860 formulations. Preferably, alkalineconditioners are used. Optionally, the substrate is rinsed with water.

Optionally, a pre-dip can then be applied to the substrate with theetched and conditioned polymer. The pre-dip can be applied, for example,by spraying or immersing the substrate in the pre-dip. Pre-dips areapplied at temperatures of 30-80° C., preferably, from 40-70° C.Pre-dips can be applied for 2-5 minutes. Conventional pre-dips can beused. Examples of pre-dips are aqueous solutions of organic salts suchas sodium potassium tartrate, sodium carbonate or sodium citrate, 0.5%to 3% sulfuric acid, aqueous nitric acid solutions with a pH of 2 orless, or an acidic solution of 25 g/L to 75 g/L sodium sulfate. Suchpre-dips are known in the art or disclosed in the electroless metalplating literature. Optionally, the substrate is rinsed with water.

A colloidal or ionic catalyst, as described above, is then applied tothe conditioned polymers of the substrate by conventional processes, forexample, by spraying or immersing the substrate in a catalyst solution.The substrate is then treated with the catalyst at temperatures from30-80° C., preferably, from 30-60° C. Catalyst dwell time can range from15 seconds to 10 minutes, preferably, from 2 minutes to 8 minutes forvertical equipment and, preferably, 25 seconds to 120 seconds forhorizontal equipment. The textured surfaces of the polymers of thesubstrate enable the catalysts to settle on the tops of the surfaces ofthe polymers as well as in the crevices and pores of the texturedsurfaces to act as seeds for metal deposits to anchor the metal depositsto the textured polymer and improve adhesion. Optionally, the substrateis rinsed with water.

Optionally, if a colloidal catalyst, such as a tin-palladium catalyst,is used in electroless metal plating, an acceleration step is done. Theacceleration step strips tin from the colloidal catalyst to expose thepalladium metal for electroless plating. Conventional accelerationsolutions include, but are not limited to, 30 wt % aqueous hydrochloricacid solution. Such solutions can be applied, for example, by sprayingor immersing the substrate in the accelerator solution at temperaturesfrom 30-80° C., preferably, from 40-70° C. Optionally, the substrate isrinsed with water.

When the catalyst is an ionic catalyst, the substrate including thecatalyst is treated with a reducing solution to reduce the metal ions totheir reduced metal state. The substrate with the ionic catalyst can be,for example, sprayed with the reducing solution or immersed in thereducing solution. The reducing solution is applied at room temperatureto 80° C., preferably from 30-60° C. Contact times between the reducingsolution and the catalyzed substrate are conventional, for example,contact times can range from 30 seconds to 5 minutes before applicationof the electroless metal plating bath.

Reducing solutions include one or more reducing agents in amountssufficient to reduce substantially all of the metal ions to metal. Suchamounts are conventional amounts and are well known by those of skill inthe art or disclosed in the electroless metal plating literature.Examples of conventional reducing agents are dimethylamine borane,sodium borohydride, ascorbic acid, iso-ascorbic acid, sodiumhypophosphite, hydrazine hydrate, formic acid and formaldehyde. Apreferred reducing agent is sodium hypophosphite.

The catalyzed substrate including the polymers are then electrolessplated with metal. The substrate can be, for example, sprayed with theelectroless metal plating bath or immersed in the electroless metalplating bath. Electroless metal plating can vary depending on thethickness of the metal desired. Electroless metal plating temperaturescan be conventional. The pH of the electroless metal plating baths aretypically alkaline. Metals which can be electroless plated include, butare not limited to, copper, copper alloys, nickel and nickel alloys.Metallization of the polymers of the substrate can be selective, suchthat only ABS, ABS-PC or combinations of ABS and ABS-PC are electrolessmetal plated.

Conventional electroless metal plating baths can be used to electrolessplate the polymers of the substrates of the present invention. Suchmetal plating baths are well known to those of skill in the art and aredisclosed in the electroless metal plating literature. Many electrolessmetal plating baths are commercially available. An example of acommercially available electroless copper plating bath is CIRCUPOSIT™880 Electroless Copper plating bath (available from Dow ElectronicMaterials). An example of a commercially available electrolessnickel-phosphorous plating bath is NIPOSIT™ PM 980 electroless nickelplating bath (available from Dow Electronic Materials).

Preferably, copper is plated on the ABS, ABS-PC, combinations thereofand additional polymers of the substrate. More preferably, copper isplated on ABS, ABS-PC or combinations thereof, even more preferably,copper is plated on ABS or ABS-PC, most preferably, copper is plated inABS. Copper plating times and temperatures can be conventional.Preferably, electroless copper plating is done at room temperature to80° C., more preferably, from 30° C. to 60° C.

Further conventional processing of the electroless metal platedsubstrates of the present invention can be done to provide a finalarticle or product. The electroless plated substrates can be plated withelectrolytic copper using conventional electrolytic copper platingmethods. An example of a commercially available electrolytic copperplating bath is ELECTROPOSIT™ 1100 VMS Copper Electroplating Solution(available from Dow Electronic Materials).

The following examples are included to further illustrate the inventionbut are not intended to limit its scope.

Example 1 (Invention) Copper Adhesion to ABS and ABS-PC Etched with anAqueous Alkaline Hydrogen Peroxide Composition of the Invention

-   1. ABS-PC coupons are etched for 6 minutes at about 70° C. in an    aqueous alkaline composition composed of 14 g/L hydrogen peroxide,    18 g/L sodium hydroxide with the balance water and the pH is 12.8,    then the etched coupons are rinsed with DI water at room temperature    for 2 minutes;-   2. The etched coupons are treated in CIRCUPOSIT™ Conditioner 3325    aqueous alkaline solution or CIRCUPOSIT™ Conditioner 231 aqueous    alkaline solution at 60° C. for 5 minutes, then rinsed with DI water    for 2 minutes;-   3. The etched and conditioned coupons are submerged in an acidic    pre-dip solution maintained at pH 2 with nitric acid for 1 minute    before applying an ionic catalyst;-   4. Each etched and conditioned coupon is immersed into ionic aqueous    alkaline catalyst solutions for 5 minutes at 40° C., wherein the    catalyst includes palladium ions complexed with 2,5-dimethylpyrazine    in one liter of water, wherein a molar ratio of complexing agent to    palladium ions is 1:1, and the catalyst is buffered with sufficient    amounts of sodium carbonate, sodium hydroxide or nitric acid to    achieve a catalyst pH of 9-9.5, then the coupons are rinsed with DI    water for 2 minutes at room temperature;-   5. The coupons are then immersed into a 0.6 g/L dimethylamine borane    and 5 g/L boric acid solution at 30° C. for 2 minutes to reduce the    palladium ions to palladium metal, then the coupons are rinsed with    DI water for 2 minutes; and-   6. The activated coupons are immersed in CIRCUPOSIT™ 880 Electroless    Copper plating baths at 35-40° C. for 15 minutes to plate    electroless copper on the coupons with a thickness of around 1 μm.

Each coupon is examined for copper plating performance. All the couponsare covered with copper and the copper deposits appear shinny anduniform. No delamination or blistering is observed.

-   7. The electroless plated copper coupons are then dried with an air    gun and stored in a desiccator until copper electroplating.-   8. A select area of 10 cm×5 cm of the electroless copper on the ABS    or ABS-PC is exposed by masking some of the area with plater's tape;-   9. A 1.5 L solution of ELECTROPOSIT™ 1100 VMS copper bath is heated    to about 28° C. and transferred to a Harring Cell maintained at    about 28° C.;-   10. Air agitation is used during the plating; Carrier TN747 is added    at 1.5 g/L and bis-(3-sulfopropyl)-disulfide at 4 ppm;-   11. A constant current of 2 A is applied to the coupons for 60    minutes to plate a copper layer with a thickness of 25 μm; and-   12. After plating is completed, the coupons are rinsed with water    and dipped in Anti-Tarnish for 30 seconds.    The samples are fully covered with shiny bright copper. No    blistering is observed. FIG. 1 is a photograph of one of the coupons    taken with a Motorola Droid camera.

Example 2 (Comparative) Copper Adhesion to ABS-PC Coupons withoutPre-Treatment of the Coupons with an Aqueous Alkaline Hydrogen PeroxideEtch Composition of the Invention

-   1. ABS-PC coupons are treated with CIRCUPOSIT™ Conditioner 3325    aqueous alkaline solution or CIRCUPOSIT™ Conditioner 231 aqueous    alkaline solution at about 60° C. for 5 minutes, then rinsed with DI    water for 2 minutes;-   2. The conditioned coupons are submerged in an acidic pre-dip    maintained at pH 2 with nitric acid for 1 minute;-   3. Each conditioned coupon is immersed into ionic aqueous alkaline    catalyst solutions for 5 minutes at about 40° C., wherein the    catalyst includes palladium ions complexed with 2,5-dimethylpyrazine    in one liter of water, wherein a molar ratio of complexing agent to    palladium ions is 1:1, and the catalyst is buffered with sufficient    amounts of sodium carbonate, sodium hydroxide or nitric acid to    achieve a catalyst pH of 9-9.5, then the coupons are rinsed with DI    water for 2 minutes at room temperature;-   4. The coupons are then immersed into a 0.6 g/L dimethylamine borane    and 5 g/L boric acid solution at about 30° C. for 2 minutes to    reduce the palladium ions to palladium metal, then the coupons are    rinsed with DI water for 2 minutes; and-   5. The activated coupons are immersed in CIRCUPOSIT™ 880 Electroless    Copper plating baths at 35-40° C. for 15 minutes to plate    electroless copper on the coupons with a thickness of around 1 μm.

Each coupon is examined for copper plating performance. All the couponsare covered with copper and the copper deposits appear shinny; however,there is extensive blistering on these samples.

-   6. The electroless plated copper coupons are then dried with an air    gun and stored in a desiccator;-   7. A select area of 10 cm×5 cm of the electroless copper on the    ABS-PC is exposed by masking other areas with plater's tape;-   8. A 1.5 L solution of ELECTROPOSIT™ 1100 VMS copper bath is heated    to about 28° C. and transferred to a Harring Cell maintained at    about 28° C.;-   9. Air agitation is applied during copper plating and Carrier TN747    is added at 1.5 g/L and bis-(3-sulfopropyl)-disulfide at 4 ppm ;-   10. A constant current of 2 A is applied to the sample for 60    minutes to a thickness of 25 μm; and-   11. After plating is completed the coupons are rinsed with water and    dipped in Anti-Tarnish for 30 seconds.    The coupons are covered with bright copper deposits but show    considerable blistering and delamination. FIG. 2 is a photograph of    one of the copper plated coupons showing the considerable    blistering.

Example 3 (Invention) Aqueous Alkaline Hydrogen Peroxide Etch of ABS

A plurality of injection molded NOVODUR™ P2MC ABS polymer couponsavailable from Styrolution Group Corporation are cleaned in a 1.5% byvolume solution of Dow product Cleaner PM-900 (available from The DowChemical Company, Midland, Mich.).

Each ABS polymer coupon is immersed in the cleaning solution for 5minutes at 50° C. The cleaned coupons are then rinsed with DI water atroom temperature for 2 minutes.

The cleaned coupons are then treated with a solvent swell which has theformulation described in Table 1.

TABLE 1 COMPONENT AMOUNT Propylene carbonate 130 g/L  EO/PO BlockCopolymer¹ 10 g/L γ-butyrolactone 60 g/L Water To one liter ¹PLURONIC ™L-64 available from Sigma Aldrich.

Each cleaned ABS coupon is then immersed in the solvent swell for 2minutes at about 40° C. The swelled ABS coupons are rinsed with DI waterat room temperature for 2 minutes. The surface of each coupon is thenanalyzed for surface morphology using SEM with an Amray 3300. FIG. 3 isa SEM of a surface of one of the solvent swelled ABS coupons at 25,000 Xwhich is substantially representative of all of the coupons analyzed bythe SEM. The hills and valleys as well as the pores observed on thesurface are due to the action of the solvent swell.

The coupons are then immersed in 1000 mL beakers containing an aqueousalkaline composition of 13.5 g/L hydrogen peroxide and 17 g/L sodiumhydroxide at about 70° C. The solutions have a pH of 12.8 at roomtemperature. The solvent swelled coupons are immersed in the aqueousalkaline solution for 9 minutes. They are then removed and rinsed withDI water and air dried. The coupons are then analyzed for surfacemorphology using SEM. FIG. 4 is a SEM at 23,808 X of a surface of one ofthe ABS coupons etched with the aqueous alkaline solution. FIG. 4 issubstantially representative of the coupons analyzed. The surfacemorphology appears rougher with higher peaks and deeper valleys than thesurface of the coupons after the application of the solvent swell asshown in FIG. 3.

Example 4 (Invention) Electroless Copper Plating of ABS and ABS-PCCoupons Etched with an Aqueous Alkaline Solution of the Invention

A plurality of injection molded NOVODUR™ P2MC ABS polymer coupons andBAYBLEND™ T45PG ABS-PC polymer blend coupons (available from Bayer) areprovided. The coupons are treated and electroless copper platedaccording to the following method:

-   1. Each coupon is treated in a cleaning solution as disclosed in    Example 3 for 5 minutes at about 50° C., then each coupon is rinsed    with DI water for 2 minutes at room temperature;-   2. The cleaned coupons are then treated with a solvent swell as    disclosed in Example 1, Table 2 for 2 minutes at about 40° C. to    swell the ABS and ABS-PC, then each coupon is rinsed with DI water    for 2 minutes at room temperature;-   3. The solvent swelled coupons are then etched for 6 minutes at    about 70° C. in an aqueous alkaline composition composed of 13.5 g/L    hydrogen peroxide, 17 g/L sodium hydroxide with the balance water    and the pH is 13, then the etched samples are rinsed with DI water    at room temperature for 2 minutes;-   4. The etched coupons are treated in CIRCUPOSIT™ Conditioner 3325    aqueous alkaline solution or CIRCUPOSIT™ Conditioner 231 aqueous    alkaline solution at about 60° C. for 5 minutes, then rinsed with DI    water for 2 minutes;-   5. The coupons are immersed in an acid pre-dip maintained at pH 2    with nitric acid for 1 minute;-   6. Each etched and conditioned coupon is immersed into CIRCUPOSIT™    6530 Catalyst which is an ionic aqueous alkaline palladium catalyst    concentrate (available from Dow Electronic Materials) for 5 minutes    at 40° C., wherein the catalyst is buffered with sufficient amounts    of sodium carbonate, sodium hydroxide or nitric acid to achieve a    catalyst pH of 9-9.5, then the coupons are rinsed with DI water for    2 minutes at room temperature;-   7. The coupons are then immersed into a 0.6 g/L dimethylamine borane    and 5 g/L boric acid solution at 30° C. for 2 minutes to reduce the    palladium ions to palladium metal, then the coupons are rinsed with    DI water for 2 minutes; and-   8. The activated coupons are immersed in CIRCUPOSIT™ 880 Electroless    Copper plating baths at 35-40° C. for 15 minutes to plate    electroless copper on the coupons with a thickness of around 1 μm.

Each coupon is examined for copper plating performance. All the couponsare covered with copper and the copper deposits appear shinny anduniform. No delamination or blistering is observed.

The electroless plated copper coupons are then dried with an air gun andstored in a desiccator prior to baking. Each electroless plated coppercoupon is baked in a conventional oven for one hour at about 70° C.

Each coupon is then analyzed for copper adhesion according to thefollowing cross-hatch tape test:

-   -   a) A crosshatch pattern is made through the film to the        substrate;    -   b) Detached flakes of coating are removed by brushing with a        soft brush;    -   c) Pressure-sensitive tape is applied over the crosshatch cut;    -   d) Tape is smoothed into place by using a pencil eraser over the        area of the incisions; and    -   e) Tape is removed by pulling it off rapidly back over itself as        close to an angle of 180°.        Except for small particles of copper on some of the tapes, no        significant portions of copper are removed from the coupons. The        coupons retain substantially all of the electroless plated        copper.

Example 5 (Invention) Peel Test for Electroless Copper Plated ABS andABS-PC with Aqueous Alkaline Hydrogen Peroxide Composition of theInvention

A plurality of injection molded NOVODUR™ P2MC ABS polymer coupons andBAYBLEND™ T45PG ABS-PC polymer blend coupons are prepared as describedin Example 4 above except the aqueous alkaline etch composition iscomposed of 14 g/L hydrogen peroxide, 18 g/L sodium hydroxide with thebalance water and the pH is 12.8 at room temperature. Copper iselectrolessly plated on the coupons as described in Example 4 to achievea copper thickness of 1 μm. The electroless plated coupons have auniform and bright deposit. No blistering is observed.

The coupons are then electrolytically plated as described in Example 4to plate an electrolytic copper layer to a thickness of 25 μm. Thecopper plated coupons have a uniform and bright copper deposit. Noblistering is observed.

Adhesion of the copper to the ABS and ABS-PC coupons is tested withINSTRON™ 90° Peel Test. Each copper plated coupon is inserted in anINSTRON™ 33R4464 apparatus with a 2 kN head pulling at a rate of 1mm/sec at a 90° angle relative to the apparatus. The copper layer ispulled by the apparatus at a constant rate of 1 mm/second and the forcerequired to maintain this rate is measured. The force at which thecopper layer is pulled from the coupon is noted and recorded for eachcopper plated coupon. The average force at which the copper is pulledfrom the coupons is determined for the ABS coupons and the ABS-PCcoupons. The average force or peel strengths for ABS coupons is 5 N/cmand for the ABS-PC coupons is 1 N/cm. Good adhesion, as accepted in theindustry, is a peel strength of 1 N/cm or greater. Accordingly, the peelstrengths for the copper layers on the ABS and ABS-PC are consideredgood and industry acceptable.

Example 6 (Comparative) Electroless Copper Plating of ABS and ABS-PCCoupons Etched with an Aqueous Solution of Hydrogen Peroxide and PeelTest

A plurality of injection molded NOVODUR™ P2MC ABS polymer coupons andBAYBLEND™ T45PG ABS-PC polymer blend coupons are prepared andelectrolessly plated with copper as described in Example 4 above exceptthe coupons are etched with an aqueous solution of hydrogen peroxidecomposed of 14 g/L hydrogen peroxide with the balance water and the pHis around 4 at room temperature. No base is included in the etchformulation.

Each coupon is examined for copper plating performance. All the couponsare covered with copper and the cooper deposits appear shinny anduniform. No delamination or blistering is observed.

The electrolessly plated copper coupons are then dried with an air gunand stored in a desiccator prior to baking. Each electrolessly platedcopper coupon is baked in a conventional oven for one hour at 70° C.

Each coupon is then analyzed for copper adhesion according to the tapetest described in Example 4. All of the tapes contain substantialamounts of copper when pulled from the coupons. Most of the coupons havesubstantially all of the plated copper removed from their surfaces.

Example 7 (Comparative) Electroless Copper Plating of ABS and ABS-PCCoupons Etched with an Aqueous Alkaline Solution of Sodium Hydroxide andPeel Test

A plurality of injection molded NOVODUR™ P2MC ABS polymer coupons andBAYBLEND™ T45PG ABS-PC polymer blend coupons are prepared andelectroless plated with copper as described in Example 4 above exceptthe coupons are etched with an aqueous alkaline solution composed of 17g/L sodium hydroxide with the balance water. The pH is around 13.3 atroom temperature. No hydrogen peroxide is included in the etchformulation.

Each coupon is examined for copper plating performance. All the couponsare covered with copper; however, the copper deposits are not uniform.There are sections of each coupon where the copper is bright andsections where the copper is matte in appearance. Some of the couponsshow blistering.

The electroless plated copper coupons are then dried with an air gun andstored in a desiccator prior to baking. Each electroless plated coppercoupon is baked in a conventional oven for one hour at 70° C.

Each coupon is then analyzed for copper adhesion according to the tapetest described in Example 4. All of the tapes contain substantialamounts of copper when pulled from the coupons. Most of the coupons havethe plated copper completely removed from their surfaces.

Example 8 (Comparative) Chromic Acid Etch-Cr(VI) of ABS

A plurality of injection molded NOVODUR™ P2MC ABS polymer coupons arecleaned in the cleaning formulation disclosed in Example 3. Each ABSpolymer coupon is immersed in the cleaning solution for 5 minutes at 50°C. The cleaned coupons are then rinsed with DI water at room temperaturefor 2 minutes and air dried.

The cleaned coupons are then treated with a solvent swell which has theformulation disclosed in Table 1 of Example 3. Each cleaned ABS couponis then immersed in the solvent swell for 2 minutes at 40° C. Theswelled ABS coupons are rinsed with DI water at room temperature for 2minutes and air dried.

The coupons are then immersed in 1000 mL beakers containing aconventional aqueous Cr(VI) chromic acid etch solution of 400 g/Lpotassium dichromate and 200 mL/L of concentrated (98wt %) sulfuricacid. The solutions have a pH of less than 1. The solvent swelledcoupons are immersed in the chromic acid etch solution for 9 minutes.They are then removed and rinsed with DI water and air dried. Thecoupons are then analyzed for surface morphology using SEM. FIG. 5 is aSEM at 12,300 X of a surface of one of the ABS coupons etched with thechromic acid etch. FIG. 5 is substantially representative of the couponsanalyzed. The surface morphology appears rough and brittle with anoverall porous surface.

Such surfaces are highly desirable for electroless metal plating becausethe rough, brittle and porous surfaces enable plated metal to anchor andattach to the surfaces to secure the metal layer and provide goodadhesion. However, chromic acid etches are hazardous to workers andenvironmentally unfriendly. Although the aqueous alkaline etch solutionof the present invention does not provide an identical brittle andporous etched surface as a chromic acid etch, as shown in Example 3 andin FIG. 4, the aqueous alkaline etch still provides substantially roughand irregular surfaces to enable good metal adhesion. At the same time,the aqueous alkaline solution of the present invention does not presentthe serious hazards to workers and the environment as the chromic acidetch, thus it is both worker and environmentally friendly. The aqueousalkaline etch solution of the present invention is an improvement overthe conventional hazardous chromic acid etch solution.

What is claimed is:
 1. A method comprising: a. providing a substratecomprising one or more organic polymers chosen from acrylonitrilebutadiene styrene and acrylonitrile butadiene styrene-polycarbonate; b.providing an aqueous alkaline etch composition composed of hydrogenperoxide and one or more sources of hydroxide ions; and c. applying theaqueous alkaline etch composition to the substrate to etch at least theone or more organic polymers chosen from acrylonitrile butadiene styreneand acrylonitrile butadiene styrene-polycarbonate.
 2. The method ofclaim 1, further comprising cleaning the substrate prior to applying theaqueous alkaline etch composition to the substrate.
 3. The method ofclaim 1, further comprising treating the substrate with a solvent swell.4. The method of claim 3, further comprising treating the solvent swelltreated and etched substrate with a conditioner.
 5. The method of claim4, further comprising contacting the solvent swell treated, etched andconditioned substrate with a catalyst.
 6. The method of claim 5, furthercomprising contacting the solvent swell treated, etched, conditioned andcatalyzed substrate with an electroless metal plating bath toelectroless plate metal on the solvent swell treated, etched andconditioned substrate.
 7. The method of claim 1, wherein the hydrogenperoxide ranges from 10 g/L to 15 g/L of the aqueous alkaline etchcomposition.
 8. The method of claim 1, wherein the one or more sourcesof hydroxide ions ranges from 5 g/L to 30 g/L.
 9. The method of claim 1,wherein the aqueous alkaline etch composition has a pH of 10 or greater.10. The method of claim 6, wherein the electroless metal plating bath isa copper, copper alloy, nickel or nickel alloy electroless plating bath.